Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Current assets:
Cash and cash equivalents	$ 502,677	$ 228,788
Receivable from collaboration partner	184,737	107,210
Deferred income tax assets	21,987	5,541
Prepaid expenses and other current assets	12,264	12,440
Restricted cash	203
Total current assets	721,868	353,979
Property and equipment, net	41,161	17,035
Intangible assets	101,000
Deferred income tax assets, noncurrent	15,176
Restricted cash, net of current	11,562	9,899
Goodwill	10,000
Other non-current assets	10,852	11,737
Total assets	911,619	392,650
Current liabilities:
Accounts payable, accrued expenses and other current liabilities	106,132	78,758
Contingent consideration	10,000
Deferred revenue	2,822	16,931
Current portion of build-to-suit lease obligation	698
Total current liabilities	119,652	95,689
Convertible Notes, net of unamortized discount of $36,598 and $50,336 at December 31, 2014 and 2013, respectively	222,140	208,414
Contingent consideration	96,000
Build-to-suit lease obligation, excluding current portion	18,711
Other non-current liabilities	5,817	11,600
Total liabilities	462,320	315,703
Commitments and contingencies (Note 14)
Stockholders' equity:
Preferred stock, $0.01 par value per share; 1,000,000 shares authorized; no shares issued and outstanding
Common stock, $0.01 par value per share; 170,000,000 shares authorized; 78,117,227 and 75,803,020 shares issued and outstanding at December 31, 2014 and 2013, respectively	781	758
Additional paid-in capital	506,227	410,350
Accumulated deficit	(57,709)	(334,161)
Total stockholders' equity	449,299	76,947
Total liabilities and stockholders' equity	$ 911,619	$ 392,650